At present, the use, and thereby the need, of purified water is growing rapidly around the world. Efforts are being made to produce pure water from less pure water than before using less chemicals, without, however, considerably raising the cost of the purification process. In addition, there is a need for the use of biodegradable or otherwise less harmful chemicals, and also chemicals which would not form compounds having detrimental health effects. Purification of raw water to produce drinking water normally includes mechanical filtration, usually biological processing, and adding the water purifying chemicals in different steps of the purification process to enhance the purification and/or to oxidize the organic and inorganic matter and organisms.
Chlorination is traditionally used to disinfect waste water. Chlorination is quite effective against bacteria, but has lower efficiency against for example viruses. In addition, chlorination gives rise to potentially toxic and mutagenic by-products, which has lead to the decrease in of chlorination as disinfection method.
Ozonation may be used to disinfect waste water. Many municipal drinking water systems kill bacteria with ozone instead of the more common chlorine. Ozone also has a very high oxidation potential. Ozone has also the ability to remove solids from wastewater by oxidation and followed by physical floatation.
Ozon sever carbon-carbon bonds and may be used to decompose organic material. Even low concentrations of ozone may be destructive to organic materials.
Activated carbon comprises small, low-volume pores that increase the surface area available for adsorption or chemical reactions. Activated carbon is used in many applications, e.g. water purification and sewage treatment, where it may be used to trap unwanted impurities.
UV-radiation has become an increasingly popular method for disinfection of water due to it being an environmentally friendly, non-chemical method. However, using UV-radiation at conventional levels often is not effective enough for reducing the level of microorganisms to acceptable levels/levels required by the authorities. To meet these requirements, users need to invest large sums in more UV-radiation capacity or in increased frequency of cleaning and/or exchange of UV-lamps.
Enteric viruses are viruses that can multiply in the gastrointestinal tract of humans or animals. More than 140 enteric viruses are known to infect humans, including viruses causing common gastrointestinal illness, hepatitis, meningitis, poliomyelitis and non-specific febrile illness. In addition, some enteric viruses have also been associated with chronic diseases, for example diabetes mellitus and chronic fatigue syndrome.
Current water disinfection processes are only able to reduce the amount of enteric viruses in the water by using high doses of chemicals.
Apart from using quite costly additives, large amounts of additives and/or not so very environmental friendly chemical additives, the known methods used for the reduction of microorganisms in water are not as effective in reducing the amount of enteric viruses.
The publication “Inactivation of enteric microorganisms with chemical disinfectants, UV irradiation and combined chemical/UV treatments” by J. Koivunen and H Heinonen-Tanski, Water Research 39 (2005) 1519-1526 discloses disinfection efficiencies between peracetic acid (PAA), hydrogen peroxide and sodium hypochlorite. Evaluation of synergistic effects with combined use of UV is also disclosed. However, combined PAA/UV disinfection did not achieve any significant synergistic effects compared to only using PAA. Peracetic acid (PAA) is an effective disinfectant against enteric bacteria, but not as effective against viruses, bacterial spores and protozoan cysts. Only by using high doses, e.g. 7-15 mg/l, of PAA can MS2 be inactivated (1-1.5 log reduction). PAA in combination with UV-irradiation has shown to be effective against enteric bacteria, but no synergistic effect is seen in the reduction of the amount of MS2, compared to PAA-treatment alone.
Micropollutants are pollutants which exists in very small concentrations in water. In natural waters, aquatic organisms are exposed to numerous inorganic and organic micropollutants (defined as synthetic and natural trace contaminants present in water at low to very low concentrations, from ng/liter to μg/liter). Organic micropollutants, which are almost exclusively man-made, are also present in natural waters. Their sources are diverse, from discharge of wastewaters and industrial installations to pesticide runoff water from agricultural lands. Aquatic organisms may thus be exposed to a mixture of numerous contaminants originating from industrial, agricultural and domestic activities. In addition, these micropollutants will not usually be removed in conventional raw water treatment processes and will hence be present in e.g. drinking water. There is an increasing amount of various organic micropollutants entering the environment. Endorcine-disrupting compounds (EDCs) are of particular concern as these trace contaminants have potential to interfere with hormonal system of living organisms. Therefore, if not removed or decomposed to a required level, these micropollutants can affect development, reproduction and fertility as well as cause other harmful effects. Among suspected EDCs are micropollutants originating from the pharmaceuticals, pesticides, personal care products, fire retardants as well as some naturally occurring compounds such as hormones.
Conventional treatment methods can remove some load of organic micropollutants, however, advanced methods are needed to remove recalcitrant micropollutants and to improve the level of decomposition. More environmentally friendly alternatives should be utilized as much as possible for these purposes. Moreover, the treatment steps and amount of additives, needed for the tertiary water treatment, should be minimized to ensure the cost-effectiveness of whole treatment system.
There still exist a need for improvement of the reduction of microorganisms like enteric viruses, and/or decomposition of organic micropollutants but also reducing the amount of additives needed in water treatments and using more environmentally friendly alternatives.